diff --git a/domain/epc_prediction/epc_prediction.py b/domain/epc_prediction/epc_prediction.py
index 072fcfc6..c582548c 100644
--- a/domain/epc_prediction/epc_prediction.py
+++ b/domain/epc_prediction/epc_prediction.py
@@ -70,6 +70,7 @@ class EpcPrediction:
         )
         self._apply_categorical_modes(predicted, comparables, target.coordinates)
         self._apply_glazing_mode(predicted, comparables, target.coordinates)
+        self._apply_ventilation_mode(predicted, comparables, target.coordinates)
         self._apply_heating_donor(predicted, comparables)
         self._apply_overrides(predicted, target)
         return predicted
@@ -139,6 +140,36 @@ class EpcPrediction:
         for window in predicted.sap_windows:
             window.glazing_type = glazing
 
+    @staticmethod
+    def _apply_ventilation_mode(
+        predicted: EpcPropertyData,
+        comparables: ComparableProperties,
+        target_coordinates: Optional[Coordinates],
+    ) -> None:
+        """Set the predicted mechanical-ventilation kind to the recency- and
+        geo-weighted cohort mode. A mechanical system (MEV/MVHR) is a new-build /
+        retrofit feature that clusters by era and street (like glazing), so a
+        recent, near neighbour is the best signal for the target's system; the
+        size-representative structural template is not (it just happens to carry
+        whatever its own cert lodged). Only the kind moves — the rest of the
+        template's `sap_ventilation` (e.g. `sheltered_sides`, derived from
+        built_form) stays. A natural-vent cohort modes to None and is left
+        natural — the §2 cascade default — so this only moves genuine MEV/MVHR
+        neighbourhoods (ADR-0029 follow-up; predicted property 721167)."""
+        ventilation = predicted.sap_ventilation
+        if ventilation is None:
+            return
+        members = comparables.members
+        weights = _combine(
+            _recency_weights(members), _geo_weights(target_coordinates, members)
+        )
+        kind = _weighted_mode(
+            (_comparable_ventilation_kind(c) for c in members), weights
+        )
+        if kind is None:
+            return
+        ventilation.mechanical_ventilation_kind = kind
+
     def confidence(
         self, comparables: ComparableProperties
     ) -> PredictionConfidence:
@@ -551,6 +582,15 @@ def _comparable_modal_glazing(
     return Counter(types).most_common(1)[0][0] if types else None
 
 
+def _comparable_ventilation_kind(
+    comparable: ComparableProperty,
+) -> Optional[str]:
+    """A comparable's mechanical-ventilation kind (the `MechanicalVentilationKind`
+    enum name, e.g. "MVHR"), or None when it lodges no system (natural)."""
+    ventilation = comparable.epc.sap_ventilation
+    return ventilation.mechanical_ventilation_kind if ventilation is not None else None
+
+
 def _main_heating_detail(comparable: ComparableProperty) -> Optional[MainHeatingDetail]:
     """The primary heating system's detail row, or None when none is lodged."""
     details = comparable.epc.sap_heating.main_heating_details